Flow meter utilizing Karman vortex street

Abstract

A fluid conduit with a rectangular cross-section is divided into two parallel conduits. A vortex generating rod is disposed perpendicularly to the flow direction in one of the conduits. An ultrasonic wave is directed perpendicularly across the conduit to detect the Karman vortex streets. A sound absorbing material is located along the portion of the conduit wall where the ultrasonic waves exist for preventing the formation of standing waves.

What we claim is: 
     
       1. A flow meter utilizing a Karman vortex street and comprising a conduit with a rectangular cross-sectional profile and divided into at least two parallel conduit portions through which a fluid to be measured flows, said at least two parallel conduit portions being substantially identical in transverse cross-sectional shape to each other, a laminar flow producing means in the upstream end of one of said conduit portions, a vortex generating member disposed in said one conduit portion perpendicularly to the direction of flow of the fluid to generate the Karman vortex street downstream thereof, a vortex detector disposed on said one conduit portion and directing an ultrasonic wave perpendicularly across the Karman vortex street and receiving the ultrasonic wave to detect the number of vortices of the Karman vortex street generated in a unit time, said vortex detecting generating an ultrasonic wave of the type which, unless preventive measures are taken, tends to generate a standing wave at the receiving side of said one conduit portion, and a sound absorbing material only on the inner wall of said one conduit portion at least along the portion where the ultrasonic waves exist for preventing the generation of a standing wave due to reflection of the said ultrasonic waves, whereby the flow rate of said fluid flowing through said plurality of conduit portions can be determined from measuring the flow rate of the portion of said fluid flowing through said one of said conduit portions.